Currently, there are spread recording media, such as a CD and a DVD, on which data can be recorded and reproduced by using a digital signal. Along with that, an information reproducing apparatus for performing a unique reproduction process by using the digital signal has been also developed. For example, in the CD and the DVD, a plurality of music songs (i.e. content data) are recorded in association with each other. More specifically, for example, music songs each of which has a predetermined reproduction time is recorded as a plurality of data groups distinguished by a track number. Thus, the information reproducing apparatus can perform cue-playback in which the head address of each music song is searched for and then the music song is reproduced, random-playback in which the reproduction order of each music song is arbitrarily changed, and the like.
Moreover, by using two or more information reproducing apparatuses and continuously reproducing the music songs while matching the beat (or the beat position, interval, accentuation of the like) of the music songs to be reproduced on the respective information reproducing apparatuses, it is possible to reproduce two or more music songs as if they are one continuous music song, or it is possible to overlap the two or more music songs. That is, it is possible to reproduce a plurality of music songs, in a row or together without bothering an audience. Such an operation is generally referred to as a mixing operation. At this time, the beat of each music song is displayed on a display screen as a beat rate or the number of beats per unit time, expressed by e.g. an automatically measured BPM (Beat Per Minute) value. A user confirms the displayed beat rate and performs the aforementioned mixing operation.
For example, a patent document 1 discloses a technology of displaying the beat rate according to a change in a reproduction speed when the reproduction speed of the music song is changed by a user's operation with respect to the beat rate automatically measured and displayed on a display.    Patent document 1: Japanese Patent Laid Open No. 2001-243717